Method of manufacturing a semiconductor device

ABSTRACT

In a method of manufacturing a semiconductor device, a fin structure is formed over a substrate. The fin structure is sculpted to have a plurality of non-etched portions and a plurality of etched portions having a narrower width than the plurality of non-etched portions. The sculpted fin structure is oxidized so that a plurality of nanowires are formed in the plurality of non-etched portions, respectively, and the plurality of etched portions are oxidized to form oxides. The plurality of nanowires are released by removing the oxides.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a divisional application of U.S. patent applicationSer. No. 16/203,378 filed Nov. 28, 2018, now U.S. Pat. No. 10,998,430,which is a divisional application of U.S. patent application Ser. No.16/104,642 filed Aug. 17, 2018, the entire disclosures of each of whichare incorporated herein by reference.

BACKGROUND

As the semiconductor industry has progressed into nanometer technologyprocess nodes in pursuit of higher device density, higher performance,and lower costs, challenges from both fabrication and design issues haveresulted in the development of three-dimensional designs, such as amulti-gate field effect transistor (FET), including a fin FET (Fin FET)and a gate-all-around (GAA) FET. In a Fin FET, a gate electrode isadjacent to three side surfaces of a channel region with a gatedielectric layer interposed therebetween. Because the gate structuresurrounds (wraps) the fin on three surfaces, the transistor essentiallyhas three gates controlling the current through the fin or channelregion. Unfortunately, the fourth side, the bottom part of the channelis far away from the gate electrode and thus is not under close gatecontrol. In contrast, in a GAA FET, all side surfaces of the channelregion are surrounded by the gate electrode, which allows for fullerdepletion in the channel region and results in less short-channeleffects due to steeper sub-threshold current swing (SS) and smallerdrain induced barrier lowering (DIBL). As transistor dimensions arecontinually scaled down to sub 10 nm technology nodes, furtherimprovements of the GAA FET are required.

BRIEF DESCRIPTION OF THE DRAWINGS

The present disclosure is best understood from the following detaileddescription when read with the accompanying figures. It is emphasizedthat, in accordance with the standard practice in the industry, variousfeatures are not drawn to scale and are used for illustration purposesonly. In fact, the dimensions of the various features may be arbitrarilyincreased or reduced for clarity of discussion.

FIG. 1 shows one of the various stages of manufacturing a semiconductorFET device according to embodiments of the present disclosure.

FIG. 2 shows one of the various stages of manufacturing a semiconductorFET device according to embodiments of the present disclosure.

FIG. 3 shows one of the various stages of manufacturing a semiconductorFET device according to embodiments of the present disclosure.

FIG. 4 shows one of the various stages of manufacturing a semiconductorFET device according to embodiments of the present disclosure.

FIG. 5 shows one of the various stages of manufacturing a semiconductorFET device according to embodiments of the present disclosure.

FIG. 6 shows one of the various stages of manufacturing a semiconductorFET device according to embodiments of the present disclosure.

FIG. 7 shows one of the various stages of manufacturing a semiconductorFET device according to embodiments of the present disclosure.

FIG. 8 shows one of the various stages of manufacturing a semiconductorFET device according to embodiments of the present disclosure.

FIGS. 9A and 9B show one of the various stages of manufacturing asemiconductor FET device according to embodiments of the presentdisclosure. FIG. 9A is a perspective view and FIG. 9B is a crosssectional view along the Y direction.

FIGS. 10A and 10B show one of the various stages of manufacturing asemiconductor FET device according to embodiments of the presentdisclosure. FIG. 10A is a perspective view and FIG. 10B is a crosssectional view along the Y direction.

FIGS. 11A and 11B show one of the various stages of manufacturing asemiconductor FET device according to embodiments of the presentdisclosure. FIG. 11A is a perspective view and FIG. 11B is a crosssectional view along the Y direction.

FIGS. 12A and 12B show one of the various stages of manufacturing asemiconductor FET device according to embodiments of the presentdisclosure. FIG. 12A is a perspective view and FIG. 12B is a crosssectional view along the Y direction.

FIGS. 13A and 13B show one of the various stages of manufacturing asemiconductor FET device according to embodiments of the presentdisclosure. FIG. 13A is a perspective view and FIG. 13B is a crosssectional view along the Y direction.

FIGS. 14A and 14B show one of the various stages of manufacturing asemiconductor FET device according to embodiments of the presentdisclosure. FIG. 14A is a perspective view and FIG. 14B is a crosssectional view along the Y direction.

FIGS. 15A-15C show one of the various stages of manufacturing asemiconductor FET device according to embodiments of the presentdisclosure. FIG. 15A is a perspective view, FIG. 15B is a crosssectional view along the Y direction and FIG. 15C is a cross sectionalview along the X direction.

FIGS. 16A-16C show one of the various stages of manufacturing asemiconductor FET device according to embodiments of the presentdisclosure. FIG. 16A is a perspective view, FIG. 16B is a crosssectional view along the Y direction and FIG. 16C is a cross sectionalview along the X direction.

FIGS. 17A-17C show one of the various stages of manufacturing asemiconductor FET device according to embodiments of the presentdisclosure. FIG. 17A is a perspective view, FIG. 17B is a crosssectional view along the Y direction and FIG. 17C is a cross sectionalview along the X direction.

FIGS. 18A-18C show one of the various stages of manufacturing asemiconductor FET device according to embodiments of the presentdisclosure. FIG. 18A is a perspective view, FIG. 18B is a crosssectional view along the Y direction and FIG. 18C is a cross sectionalview along the X direction.

FIGS. 19A and 19B show one of the various stages of manufacturing asemiconductor FET device according to embodiments of the presentdisclosure. FIG. 19A is a perspective view and FIG. 19B is a crosssectional view along the Y direction.

FIGS. 20A and 20B show one of the various stages of manufacturing asemiconductor FET device according to embodiments of the presentdisclosure. FIG. 20A is a perspective view and FIG. 20B is a crosssectional view along the Y direction.

FIGS. 21A and 21B show one of the various stages of manufacturing asemiconductor FET device according to embodiments of the presentdisclosure. FIG. 21A is a perspective view and FIG. 21B is a crosssectional view along the Y direction.

FIGS. 22A and 22B show one of the various stages of manufacturing asemiconductor FET device according to embodiments of the presentdisclosure. FIG. 22A is a perspective view and FIG. 22B is a crosssectional view along the Y direction.

FIGS. 23A and 23B show one of the various stages of manufacturing asemiconductor FET device according to embodiments of the presentdisclosure. FIG. 23A is a perspective view and FIG. 23B is a crosssectional view along the Y direction.

FIGS. 24A and 24B show one of the various stages of manufacturing asemiconductor FET device according to embodiments of the presentdisclosure. FIG. 24A is a perspective view and FIG. 24B is a crosssectional view along the Y direction.

FIGS. 25A and 25B show one of the various stages of manufacturing asemiconductor FET device according to embodiments of the presentdisclosure. FIG. 25A is a perspective view and FIG. 25B is a crosssectional view along the Y direction.

FIGS. 26A and 26B show one of the various stages of manufacturing asemiconductor FET device according to embodiments of the presentdisclosure. FIG. 26A is a perspective view and FIG. 26B is a crosssectional view along the Y direction.

FIGS. 27A and 27B show one of the various stages of manufacturing asemiconductor FET device according to embodiments of the presentdisclosure. FIG. 27A is a perspective view and FIG. 27B is a crosssectional view along the Y direction.

FIGS. 28A and 28B show one of the various stages of manufacturing asemiconductor FET device according to embodiments of the presentdisclosure. FIG. 28A is a perspective view and FIG. 28B is a crosssectional view along the Y direction.

FIGS. 29A and 29B show one of the various stages of manufacturing asemiconductor FET device according to embodiments of the presentdisclosure. FIG. 29A is a perspective view and FIG. 29B is a crosssectional view along the Y direction.

FIGS. 30A and 30B show one of the various stages of manufacturing asemiconductor FET device according to embodiments of the presentdisclosure. FIG. 30A is a perspective view and FIG. 30B is a crosssectional view along the Y direction.

FIGS. 31A and 31B show one of the various stages of manufacturing asemiconductor FET device according to embodiments of the presentdisclosure. FIG. 31A is a perspective view and FIG. 31B is a crosssectional view along the Y direction.

FIGS. 32A and 32B show one of the various stages of manufacturing asemiconductor FET device according to embodiments of the presentdisclosure. FIG. 32A is a perspective view and FIG. 32B is a crosssectional view along the Y direction.

FIGS. 33A and 33B show one of the various stages of manufacturing asemiconductor FET device according to embodiments of the presentdisclosure. FIG. 33A is a perspective view and FIG. 33B is a crosssectional view along the Y direction.

FIGS. 34A and 34B show one of the various stages of manufacturing asemiconductor FET device according to embodiments of the presentdisclosure. FIG. 34A is a perspective view and FIG. 34B is a crosssectional view along the Y direction.

FIGS. 35A and 35B show one of the various stages of manufacturing asemiconductor FET device according to other embodiments of the presentdisclosure. FIG. 35A is a perspective view and FIG. 35B is a crosssectional view along the Y direction.

FIGS. 36A and 36B show one of the various stages of manufacturing asemiconductor FET device according to other embodiments of the presentdisclosure. FIG. 36A is a perspective view and FIG. 36B is a crosssectional view along the Y direction.

FIGS. 37A and 37B show one of the various stages of manufacturing asemiconductor FET device according to other embodiments of the presentdisclosure. FIG. 37A is a perspective view and FIG. 37B is a crosssectional view along the Y direction.

FIGS. 38A and 38B show one of the various stages of manufacturing asemiconductor FET device according to other embodiments of the presentdisclosure. FIG. 38A is a perspective view and FIG. 38B is a crosssectional view along the Y direction.

FIGS. 39A and 39B show one of the various stages of manufacturing asemiconductor FET device according to other embodiments of the presentdisclosure. FIG. 39A is a perspective view and FIG. 39B is a crosssectional view along the Y direction.

FIGS. 40A and 40B show one of the various stages of manufacturing asemiconductor FET device according to other embodiments of the presentdisclosure. FIG. 40A is a perspective view and FIG. 40B is a crosssectional view along the Y direction.

FIGS. 41A and 41B show one of the various stages of manufacturing asemiconductor FET device according to other embodiments of the presentdisclosure. FIG. 40A is a perspective view and FIG. 40B is a crosssectional view along the Y direction.

FIG. 42 shows one of the various stages of manufacturing a semiconductorFET device according to other embodiments of the present disclosure.

FIG. 43 shows one of the various stages of manufacturing a semiconductorFET device according to other embodiments of the present disclosure.

FIG. 44 shows one of the various stages of manufacturing a semiconductorFET device according to other embodiments of the present disclosure.

FIG. 45 shows one of the various stages of manufacturing a semiconductorFET device according to other embodiments of the present disclosure.

FIG. 46 shows one of the various stages of manufacturing a semiconductorFET device according to other embodiments of the present disclosure.

FIG. 47 shows one of the various stages of manufacturing a semiconductorFET device according to other embodiments of the present disclosure.

FIG. 48 shows one of the various stages of manufacturing a semiconductorFET device according to other embodiments of the present disclosure.

FIG. 49 shows one of the various stages of manufacturing a semiconductorFET device according to other embodiments of the present disclosure.

FIG. 50 shows one of the various stages of manufacturing a semiconductorFET device according to other embodiments of the present disclosure.

FIG. 51 shows one of the various stages of manufacturing a semiconductorFET device according to other embodiments of the present disclosure.

FIG. 52 shows one of the various stages of manufacturing a semiconductorFET device according to other embodiments of the present disclosure.

FIGS. 53A and 53B show one of the various stages of manufacturing asemiconductor FET device according to other embodiments of the presentdisclosure. FIG. 53A is a perspective view and FIG. 53B is a crosssectional view along the Y direction.

FIGS. 54A and 54B show one of the various stages of manufacturing asemiconductor FET device according to other embodiments of the presentdisclosure. FIG. 54A is a perspective view and FIG. 54B is a crosssectional view along the Y direction.

FIGS. 55A and 55B show one of the various stages of manufacturing asemiconductor FET device according to other embodiments of the presentdisclosure. FIG. 55A is a perspective view and FIG. 55B is a crosssectional view along the Y direction.

FIGS. 56A and 56B show one of the various stages of manufacturing asemiconductor FET device according to other embodiments of the presentdisclosure. FIG. 56A is a perspective view and FIG. 56B is a crosssectional view along the Y direction.

FIGS. 57A and 57B show one of the various stages of manufacturing asemiconductor FET device according to other embodiments of the presentdisclosure. FIG. 57A is a perspective view and FIG. 57B is a crosssectional view along the Y direction.

FIGS. 58A and 58B show one of the various stages of manufacturing asemiconductor FET device according to other embodiments of the presentdisclosure. FIG. 58A is a perspective view and FIG. 58B is a crosssectional view along the Y direction.

FIGS. 59A and 59B show one of the various stages of manufacturing asemiconductor FET device according to other embodiments of the presentdisclosure. FIG. 59A is a perspective view and FIG. 59B is a crosssectional view along the Y direction.

FIGS. 60A and 60B show one of the various stages of manufacturing asemiconductor FET device according to other embodiments of the presentdisclosure. FIG. 60A is a perspective view and FIG. 60B is a crosssectional view along the Y direction.

FIGS. 61A and 61B show one of the various stages of manufacturing asemiconductor FET device according to other embodiments of the presentdisclosure. FIG. 61A is a perspective view and FIG. 61B is a crosssectional view along the Y direction.

FIGS. 62A and 62B show one of the various stages of manufacturing asemiconductor FET device according to other embodiments of the presentdisclosure. FIG. 62A is a perspective view and FIG. 62B is a crosssectional view along the Y direction.

FIGS. 63A and 63B show one of the various stages of manufacturing asemiconductor FET device according to other embodiments of the presentdisclosure. FIG. 63A is a perspective view and FIG. 63B is a crosssectional view along the Y direction.

FIGS. 64A and 64B show one of the various stages of manufacturing asemiconductor FET device according to other embodiments of the presentdisclosure. FIG. 64A is a perspective view and FIG. 64B is a crosssectional view along the Y direction.

FIGS. 65A and 65B show one of the various stages of manufacturing asemiconductor FET device according to other embodiments of the presentdisclosure. FIG. 65A is a perspective view and FIG. 65B is a crosssectional view along the Y direction.

FIGS. 66A and 66B show one of the various stages of manufacturing asemiconductor FET device according to other embodiments of the presentdisclosure. FIG. 66A is a perspective view and FIG. 66B is a crosssectional view along the Y direction.

FIGS. 67A and 67B show one of the various stages of manufacturing asemiconductor FET device according to other embodiments of the presentdisclosure. FIG. 67A is a perspective view and FIG. 67B is a crosssectional view along the Y direction.

FIGS. 68A and 68B show one of the various stages of manufacturing asemiconductor FET device according to other embodiments of the presentdisclosure. FIG. 68A is a perspective view and FIG. 68B is a crosssectional view along the Y direction.

FIGS. 69A and 69B show one of the various stages of manufacturing asemiconductor FET device according to other embodiments of the presentdisclosure. FIG. 69A is a perspective view and FIG. 69B is a crosssectional view along the Y direction.

FIGS. 70A and 70B show one of the various stages of manufacturing asemiconductor FET device according to other embodiments of the presentdisclosure. FIG. 70A is a perspective view and FIG. 70B is a crosssectional view along the Y direction.

FIGS. 71A and 71B show one of the various stages of manufacturing asemiconductor FET device according to other embodiments of the presentdisclosure. FIG. 71A is a perspective view and FIG. 71B is a crosssectional view along the Y direction.

FIGS. 72A and 72B show one of the various stages of manufacturing asemiconductor FET device according to other embodiments of the presentdisclosure. FIG. 72A is a perspective view and FIG. 72B is a crosssectional view along the Y direction.

FIGS. 73A and 73B show one of the various stages of manufacturing asemiconductor FET device according to other embodiments of the presentdisclosure. FIG. 73A is a perspective view and FIG. 73B is a crosssectional view along the Y direction.

FIGS. 74A and 74B show one of the various stages of manufacturing asemiconductor FET device according to other embodiments of the presentdisclosure. FIG. 74A is a perspective view and FIG. 74B is a crosssectional view along the Y direction.

FIGS. 75A and 75B show one of the various stages of manufacturing asemiconductor FET device according to other embodiments of the presentdisclosure. FIG. 75A is a perspective view and FIG. 75B is a crosssectional view along the Y direction.

FIGS. 76A and 76B show one of the various stages of manufacturing asemiconductor FET device according to other embodiments of the presentdisclosure. FIG. 76A is a perspective view and FIG. 76B is a crosssectional view along the Y direction.

FIGS. 77A and 77B show one of the various stages of manufacturing asemiconductor FET device according to other embodiments of the presentdisclosure. FIG. 77A is a perspective view and FIG. 77B is a crosssectional view along the Y direction.

FIG. 78 shows one of the various stages of manufacturing a semiconductorFET device according to another embodiment of the present disclosure.

FIGS. 79A and 79B show one of the various stages of manufacturing asemiconductor FET device according to other embodiments of the presentdisclosure. FIG. 79A is a perspective view and FIG. 79B is a crosssectional view along the Y direction.

FIGS. 80A and 80B show one of the various stages of manufacturing asemiconductor FET device according to other embodiments of the presentdisclosure. FIG. 80A is a perspective view and FIG. 80B is a crosssectional view along the Y direction.

FIGS. 81A and 81B show one of the various stages of manufacturing asemiconductor FET device according to other embodiments of the presentdisclosure. FIG. 81A is a perspective view and FIG. 81B is a crosssectional view along the Y direction.

FIGS. 82A and 82B show one of the various stages of manufacturing asemiconductor FET device according to other embodiments of the presentdisclosure. FIG. 82A is a perspective view and FIG. 82B is a crosssectional view along the Y direction.

FIGS. 83A and 83B show one of the various stages of manufacturing asemiconductor FET device according to other embodiments of the presentdisclosure. FIG. 83A is a perspective view and FIG. 83B is a crosssectional view along the Y direction.

FIGS. 84A and 84B show one of the various stages of manufacturing asemiconductor FET device according to other embodiments of the presentdisclosure. FIG. 84A is a perspective view and FIG. 84B is a crosssectional view along the Y direction.

FIGS. 85A and 85B show one of the various stages of manufacturing asemiconductor FET device according to other embodiments of the presentdisclosure. FIG. 85A is a perspective view and FIG. 85B is a crosssectional view along the Y direction.

FIGS. 86A and 86B show one of the various stages of manufacturing asemiconductor FET device according to other embodiments of the presentdisclosure. FIG. 86A is a perspective view and FIG. 86B is a crosssectional view along the Y direction.

FIGS. 87A-87C show one of the various stages of manufacturing asemiconductor FET device according to other embodiments of the presentdisclosure. FIG. 87A is a perspective view, and FIGS. 87B and 87C arecross sectional views along the Y direction.

FIG. 88 shows one of the various stages of manufacturing a semiconductorFET device according to other embodiments of the present disclosure.

FIG. 89 shows one of the various stages of manufacturing a semiconductorFET device according to other embodiments of the present disclosure.

FIG. 90 shows one of the various stages of manufacturing a semiconductorFET device according to other embodiments of the present disclosure.

FIG. 91 shows one of the various stages of manufacturing a semiconductorFET device according to other embodiments of the present disclosure.

FIG. 92 shows one of the various stages of manufacturing a semiconductorFET device according to other embodiments of the present disclosure.

FIG. 93 shows one of the various stages of manufacturing a semiconductorFET device according to other embodiments of the present disclosure.

FIG. 94 shows one of the various stages of manufacturing a semiconductorFET device according to other embodiments of the present disclosure.

FIG. 95 shows one of the various stages of manufacturing a semiconductorFET device according to other embodiments of the present disclosure.

FIG. 96 shows one of the various stages of manufacturing a semiconductorFET device according to other embodiments of the present disclosure.

FIG. 97 shows one of the various stages of manufacturing a semiconductorFET device according to other embodiments of the present disclosure.

FIG. 98 shows one of the various stages of manufacturing a semiconductorFET device according to other embodiments of the present disclosure.

FIG. 99 shows one of the various stages of manufacturing a semiconductorFET device according to other embodiments of the present disclosure.

FIG. 100 shows one of the various stages of manufacturing asemiconductor FET device according to other embodiments of the presentdisclosure.

DETAILED DESCRIPTION

It is to be understood that the following disclosure provides manydifferent embodiments, or examples, for implementing different featuresof the invention. Specific embodiments or examples of components andarrangements are described below to simplify the present disclosure.These are, of course, merely examples and are not intended to belimiting. For example, dimensions of elements are not limited to thedisclosed range or values, but may depend upon process conditions and/ordesired properties of the device. Moreover, the formation of a firstfeature over or on a second feature in the description that follows mayinclude embodiments in which the first and second features are formed indirect contact, and may also include embodiments in which additionalfeatures may be formed interposing the first and second features, suchthat the first and second features may not be in direct contact. Variousfeatures may be arbitrarily drawn in different scales for simplicity andclarity.

Further, spatially relative terms, such as “beneath,” “below,” “lower,”“above,” “upper” and the like, may be used herein for ease ofdescription to describe one element or feature's relationship to anotherelement(s) or feature(s) as illustrated in the figures. The spatiallyrelative terms are intended to encompass different orientations of thedevice in use or operation in addition to the orientation depicted inthe figures. The apparatus may be otherwise oriented (rotated 90 degreesor at other orientations) and the spatially relative descriptors usedherein may likewise be interpreted accordingly. In addition, the term“being made of” may mean either “comprising” or “consisting of”

In the present disclosure, GAA FETs and methods for fabricating the sameare provided. In this disclosure, nanowire structures for channelregions are formed without making a stack of semiconductor layers.

FIGS. 1-34B show an exemplary sequential operation for manufacturing theGAA FET according to an embodiment of the present disclosure. It isunderstood that additional operations can be provided before, during,and after processes shown by FIGS. 1-34B, and some of the operationsdescribed below can be replaced or eliminated, for additionalembodiments of the method. The order of the operations/processes may beinterchangeable.

As shown in FIGS. 1 and 2, a semiconductor fin structure 20 is formedover a semiconductor substrate 10. Although one fin structure 20 isprovided over the substrate 10, the number of fin structures is notlimited to one, and may be two or more. In some embodiments, thesubstrate 10 includes a single crystalline semiconductor layer on atleast its surface portion. The substrate 10 may comprise a singlecrystalline semiconductor material such as, but not limited to Si, Ge,SiGe, GaAs, InSb, GaP, GaSb, InAlAs, InGaAs, GaSbP, GaAsSb and InP. Incertain embodiments, the substrate 10 is made of crystalline Si.

The substrate 10 may include in its surface region, one or more bufferlayers (not shown). The buffer layers can serve to gradually change thelattice constant from that of the substrate to that of the source/drainregions. The buffer layers may be formed from epitaxially grown singlecrystalline semiconductor materials such as, but not limited to Si, Ge,GeSn, SiGe, GaAs, InSb, GaP, GaSb, InAlAs, InGaAs, GaSbP, GaAsSb, GaN,GaP, and InP. In a particular embodiment, the substrate 10 comprisessilicon germanium (SiGe) buffer layers epitaxially grown on the siliconsubstrate 10. The germanium concentration of the SiGe buffer layers mayincrease from 1 atomic % germanium for the bottom-most buffer layer to99 atomic % germanium for the top-most buffer layer. In someembodiments, the germanium concentration of the SiGe buffer layers mayincrease from 30 atomic % germanium for the bottom-most buffer layer to70 atomic % germanium for the top-most buffer layer.

The fin structure 20 may be patterned by any suitable method. Forexample, the structures may be patterned using one or morephotolithography processes, including double-patterning ormulti-patterning processes. Generally, double-patterning ormulti-patterning processes combine photolithography and self-alignedprocesses, allowing patterns to be created that have, for example,pitches smaller than what is otherwise obtainable using a single, directphotolithography process. For example, in one embodiment, a sacrificiallayer is formed over a substrate and patterned using a photolithographyprocess. Spacers are formed alongside the patterned sacrificial layerusing a self-aligned process. The sacrificial layer is then removed, andthe remaining spacers may then be used to pattern the stacked finstructure.

In some embodiments, a hard mask pattern 25 is formed over the substrate10 as shown in FIG. 1 and then the substrate 10 is patterned by one ormore lithography and etching operations as set forth above.

In some embodiments, the hard mask 25 includes a first mask layer and asecond mask layer. The first mask layer is a pad oxide layer made of asilicon oxide, which can be formed by a thermal oxidation. The secondmask layer is made of a silicon nitride (SiN), which is formed bychemical vapor deposition (CVD), including low pressure CVD (LPCVD) andplasma enhanced CVD (PECVD), physical vapor deposition (PVD), atomiclayer deposition (ALD), or other suitable process. The mask layer ispatterned into the hard mask pattern 25 by using patterning operationsincluding photo-lithography and etching. As shown in FIG. 2, the finstructure 20 extends in the X direction. In some embodiments, one ormore dummy fin structures are formed on both sides of the fin structure20 to improve pattern fidelity in the patterning operations. The widthof the fin structure along the Y direction is in a range from about 10nm to about 40 nm in some embodiments, and is in a range from about 20nm to about 30 nm in other embodiments. The height along the Z directionof the fin structure 20 is in a range from about 10 nm to about 200 nm.

After the fin structure 20 is formed, an insulating material layerincluding one or more layers of insulating material is formed over thesubstrate so that the fin structure is fully embedded in the insulatinglayer. The insulating material for the insulating layer may includesilicon oxide, silicon nitride, silicon oxynitride (SiON), SiOCN, SiCN,fluorine-doped silicate glass (FSG), or a low-k dielectric material,formed by LPCVD (low pressure chemical vapor deposition), plasma-CVD orflowable CVD. An anneal operation may be performed after the formationof the insulating layer. Then, a planarization operation, such as achemical mechanical polishing (CMP) method and/or an etch-back method,is performed such that the upper surface of the hard mask 25 is exposedfrom the insulating material layer. In some embodiments, one or more finliner layers are formed over the fin structure before forming theinsulating material layer. The fin liner layers include one or more ofSiN or a silicon nitride-based material (e.g., SiON, SiCN or SiOCN). Insome embodiments, the liner layers may be deposited through one or moreprocesses such as physical vapor deposition (PVD), chemical vapordeposition (CVD), or atomic layer deposition (ALD), although anyacceptable process may be utilized.

Then, as shown in FIG. 3, the insulating material layer is recessed toform an isolation insulating layer 30 so that the upper portion of thefin structure 20 is exposed. The isolation insulating layer 30 is alsocalled a shallow trench isolation (STI).

After the isolation insulating layer 40 is formed, a sacrificial (dummy)gate structure 40 is formed, as shown in FIGS. 4 and 5. FIG. 5illustrates a structure after a first sacrificial gate structure 40 isformed over the exposed fin structure 20. The first sacrificial gatestructure 40 is formed over a portion of the fin structure which is tobe a channel region. The sacrificial gate structure defines the channelregion of the GAA FET. The first sacrificial gate structure 40 includesa sacrificial gate dielectric layer 42 and a first sacrificial gateelectrode layer 44. The sacrificial gate dielectric layer 42 includesone or more layers of insulating material, such as a silicon oxide-basedmaterial. In one embodiment, silicon oxide formed by CVD is used. Thethickness of the sacrificial gate dielectric layer 42 is in a range fromabout 1 nm to about 5 nm in some embodiments. In some embodiments, thehard mask 25 is removed before the first sacrificial gate structure 40is formed.

The first sacrificial gate structure 40 is formed by first blanketdepositing the sacrificial gate dielectric layer 42 over the finstructures. A first sacrificial gate electrode layer 44 is then blanketdeposited on the sacrificial gate dielectric layer and over the finstructures, such that the fin structures are fully embedded in the firstsacrificial gate electrode layer, as shown in FIG. 4. The firstsacrificial gate electrode layer includes silicon such aspolycrystalline silicon or amorphous silicon. The thickness of the firstsacrificial gate electrode layer is in a range from about 10 nm to about200 nm in some embodiments. In some embodiments, the first sacrificialgate electrode layer is subjected to a planarization operation. Thesacrificial gate dielectric layer and the first sacrificial gateelectrode layer are deposited using CVD, including LPCVD and PECVD, PVD,ALD, or other suitable process. Subsequently, a mask layer (not shown)is formed over the first sacrificial gate electrode layer. The masklayer includes a pad SiN layer and a silicon oxide mask layer in someembodiments.

Next, a patterning operation is performed on the mask layer and thefirst sacrificial gate electrode layer is patterned into the firstsacrificial gate structure 40, as shown in FIG. 5. By patterning thesacrificial gate structure, the fin structure 20 is partially exposed onopposite sides of the first sacrificial gate structure 40, therebydefining source/drain (S/D) regions, as shown in FIG. 5. In thisdisclosure, a source and a drain are interchangeably used and thestructures thereof are substantially the same. In FIG. 5, onesacrificial gate structure is formed, but the number of the sacrificialgate structures is not limited to one. Two or more sacrificial gatestructures are arranged in the X direction in some embodiments. Incertain embodiments, one or more dummy sacrificial gate structures areformed on both sides of the sacrificial gate structures to improvepattern fidelity.

After the sacrificial gate structure is formed, a first insulating layer46 for sidewall spacers is formed as shown in FIG. 6. In someembodiments, the first insulating layer 46 is conformally formed overthe exposed fin structure 20 and the first sacrificial gate structure40. The first insulating layer 46 includes one or more layers ofinsulating material, such as SiN, SiON, SiOC, SiOCN and SiCN or anyother suitable insulating material. SiC may be used as well. Theinsulating layer 46 can be formed by ALD or CVD, or any other suitablemethod. Then, as shown in FIG. 7, anisotropic etching is performed toform sidewall spacers 45.

Further, as shown in FIG. 8, a SD (source/drain) cover layer 50 isformed as shown in FIG. 8. In some embodiments, the SD cover layer 50includes one or more layers of SiN, SiCN, SiON and SiC. Next, as shownin FIGS. 9A and 9B, the SD cover layer 50 is planarized by using anetch-back operation and/or a CMP operation, to expose the upper surfaceof the first sacrificial gate electrode layer 44. FIG. 9B is a crosssectional view along the Y direction cutting the sacrificial gatestructure. In some embodiments, the SD cover layer 50 is made of adifferent material than the sidewall spacers 45.

Then, as shown in FIGS. 10A and 10B, the first sacrificial gateelectrode layer 44 and the sacrificial gate dielectric layer 42 areremoved to form a gate space 52. In the gate space 52, the fin structure20 with the hard mask 25 is exposed in some embodiments. When the firstsacrificial gate electrode layer 44 is polysilicon, a wet etchant suchas a TMAH (tetramethylammonium hydroxide) solution can be used toselectively remove the first sacrificial gate electrode layer 44. Thesacrificial gate dielectric layer 42 is thereafter removed using plasmadry etching and/or wet etching operations.

Next, as shown in FIGS. 11A and 11B, a second insulating layer 55 isformed over the gate space and the SD cover layer, and the gate space 52is filled with the second insulating layer 55. The second insulatinglayer 55 is made of a different material than the SD cover layer and ismade of a silicon oxide based material, such as silicon oxide, SiON andSiOC in some embodiments. In some embodiments, the second insulatinglayer 55 is made of a different material than the sidewall spacers 45.

Further, as shown in FIGS. 12A and 12B, the second insulating layer 55is recessed such that an upper portion of the fin structure and the hardmask 25 are exposed. The recess etching includes one or more dry etchingand/or wet etching operations. The exposed amount D1, which is adistance between the top of the fin structure 20 and the upper surfaceof the recessed second insulating layer 55, is about 5 nm to about 30 nmin some embodiments.

Then, a first channel cover layer 60 made of one of SiN, SiCN, SiON andSiC is formed as shown in FIGS. 13A and 13B. In some embodiments, thefirst channel cover layer 60 is made of the same material as the SDcover layer 50. In other embodiments, the first channel cover layer 60is made of the different material from the SD cover layer 50.

Further, as shown in FIGS. 14A and 14B, anisotropic etching is performedto form first channel sidewall spacers 61. Then, as shown in FIGS.15A-15C, the second insulating layer 55 is further recessed by one ormore dry etching and/or wet etching to expose a part of the finstructure 20. FIG. 15B is a cross sectional view along the Y directioncutting the fin structure 20 and FIG. 15C is a cross sectional viewalong the X direction at the interface between the fin structure 20 andthe second insulating layer 55. The exposed amount D2, which is adistance between the bottom of the first channel sidewall spacers 61 andthe upper surface of the recessed second insulating layer 55, is about 5nm to about 30 nm in some embodiments.

Next, as shown in FIGS. 16A-16B, the exposed portion of the finstructure 20 is sculpted by etching to reduce the width of the exposedportion. In some embodiments, wet etching using TMAH or KOH is used toetch the exposed portion. In other embodiments, dry etching is used. Bythis etching, the narrowest portion 22 of the sculpted fin structure 20has a width W1 which is about 30% to about 70% of the original width ofthe fin structure 20 in some embodiments. Further, as shown in FIG. 16C,portions of the fin structures under the sidewall spacers 45 are alsohorizontally etched in the X direction.

Then, as shown in FIGS. 17A-17C, the second insulating layer 55 isfurther recessed to further expose a portion of the fin structure 20.The recess etching includes one or more dry etching and/or wet etchingoperations. The exposed amount D3 is substantially equal to or smallerthan D1 in some embodiments. The exposed amount D3 is about 5 nm toabout 20 nm in some embodiments.

Then, a second channel cover layer 62 made of one of SiN, SiCN, SiON andSiC is formed as shown in FIGS. 18A-18C. In some embodiments, the secondchannel cover layer 62 is made of the same material as the first channelcover layer 60. As shown in FIG. 18C, the second channel cover layer 62is filled in the recessed portion 22 of the fin structure under thesidewall spacers 45. In some embodiments, the first channel sidewallspacer 61 is removed before the formation of the second cover layer 62.In other embodiments, the first channel sidewall spacer 61 is notremoved before the formation of the second cover layer 62.

Further, as shown in FIGS. 19A and 19B, anisotropic etching is performedto form second channel sidewall spacers 63. Then, as shown in FIGS. 20Aand 20B, the second insulating layer 55 is further recessed by one ormore dry etching and/or wet etching to expose a part of the finstructure 20. The exposed amount D4, which is a distance between thebottom of the second channel sidewall spacers 63 and the upper surfaceof the recessed second insulating layer 55, is about 5 nm to about 20 nmin some embodiments. In some embodiments, D4 is substantially equal toD2.

Next, as shown in FIGS. 21A and 21B, the exposed portion of the finstructure 20 is partially etched to reduce the width of the exposedportion, similar to FIGS. 17A-17C. Then, as shown in FIGS. 22A and 22B,the second insulating layer 55 is further recessed to further expose aportion of the fin structure 20, similar to FIGS. 18A and 18B. Theexposed amount D5 is substantially equal to D3 in some embodiments.

Then, a third channel cover layer 64 made of one of SiN, SiCN, SiON andSiC is formed as shown in FIGS. 23A and 23B, similar to FIGS. 18A-18C.In some embodiments, the third channel cover layer 64 is made of thesame material as the first channel cover layer 60. In some embodiments,the second channel sidewall spacer 63 is removed before the formation ofthe third channel cover layer 64. In other embodiments, the secondchannel sidewall spacer 63 is not removed before the formation of thethird channel cover layer 64. Further, as shown in FIGS. 24A and 24B,anisotropic etching is performed to form third channel sidewall spacers65, similar to FIGS. 19A and 19B. Then, as shown in FIGS. 25A and 25B,the second insulating layer 55 is further recessed by one or more dryetching and/or wet etching to expose a part of the fin structure 20,similar to FIGS. 20A and 20B. The exposed amount D6, which is a distancebetween the bottom of the third channel sidewall spacers 65 and theupper surface of the recessed second insulating layer 55, is about 5 nmto about 20 nm in some embodiments. In some embodiments, D6 issubstantially equal to D2. Next, as shown in FIGS. 26A and 26B, theexposed portion of the fin structure 20 is etched to reduce the width ofthe exposed portion, similar to FIGS. 17A-17C.

The operations of forming a channel cover layer, recessing the secondinsulating layer and etching the exposed fin structure are repeated bythe desired number of times, for example 3-10 times in total. Thus, asculpted fin structure is formed in the channel region.

Subsequently, as shown in FIGS. 27A and 27B, after the last channelcover layer is formed over the sculpted fin structure and last channelsidewall spacers 67 are formed, a sacrificial layer 69 is formed, andthen one or more planarization operations, such as an etch backoperation and a CMP operation, are performed to form a secondsacrificial gate structure 70, as shown in FIGS. 28A and 28B. In someembodiments, the second sacrificial gate structure 70 is made ofpolysilicon or amorphous silicon formed by CVD.

Then, as shown in FIGS. 29A and 29B, the SD cover layer 50 and hard mask25 are removed to expose a source/drain region of the fin structure 20.After a source/drain epitaxial layer 80 is formed over the source/drainregion of the fin structure 20, an interlayer dielectric (ILD) layer 85is formed, as shown in FIGS. 30A and 30B. The source/drain epitaxiallayer 80 includes one or more layers of Si, SiP, SiC and SiCP for ann-channel FET or Si, SiGe and Ge for a p-channel FET. For the n-channelFET, phosphorus (P) may also be contained in the source/drain. For thep-channel FET, boron (B) may also be contained in the source/drain. Thesource/drain epitaxial layer 80 is formed by an epitaxial growth methodusing CVD, ALD or molecular beam epitaxy (MBE). In some embodiments, thefin structures of the source/drain regions are recessed down to aboutthe upper surface of the isolation insulating layer 30, and then thesource/drain epitaxial layer 80 is formed. The materials for the ILDlayer 85 include compounds comprising Si, O, C and/or H, such as siliconoxide, SiON, SiCOH and SiOC. Organic materials, such as polymers, may beused for the ILD layer 85. After the material for the ILD layer 85 isformed, a planarization operation, such as CMP, is performed, so thatthe top portion of the second sacrificial gate structure 70 is exposed.Then, the second sacrificial gate structure 70 is removed, and the hardmask 25 is removed, as shown in FIGS. 31A and 31B.

Next, the exposed sculpted fin structure 20 with etched portions isoxidized to form nanowires 27 separated by an oxide 90. In someembodiments, as shown in FIGS. 32A and 32B, four nanowires 27 a-27 d areformed, but the number of nanowires is not limited to four. Theoxidization process is performed such that the etched narrow portions ofthe sculpted fin structure 20 are fully oxidized, while non-etchedportions of the sculpted fin structure 20 are only partially oxidized.In some embodiments, one or more of a thermal oxidization process, aplasma oxidization process and/or a chemical oxidization process areutilized. In some embodiments, a process temperature of the thermaloxidization is in a range from about 500° C. to about 800° C. In someembodiments, a process temperature of the plasma oxidization is in arange from about 300° C. to about 500° C. The ILD layer 85 protects thesource/drain structures 80 during the oxidation of the exposed finstructure 20.

Then, as shown in FIGS. 33A and 33B, the oxide 90 is removed to releasethe semiconductor nanowires 27. The oxide 90 can be removed by suitabledry etching and/or wet etching operations. After the semiconductornanowires 27 are formed, a gate dielectric layer 102 is formed aroundeach nanowire 27 (channel), and a gate electrode layer 104 is formed onthe gate dielectric layer 102, as shown in FIGS. 34A and 34B.

In certain embodiments, the gate dielectric layer 102 includes one ormore layers of a dielectric material, such as silicon oxide, siliconnitride, or high-k dielectric material, other suitable dielectricmaterial, and/or combinations thereof. Examples of high-k dielectricmaterial include HfO₂, HfSiO, HfSiON, HfTaO, HfSiO, HfZrO, zirconiumoxide, aluminum oxide, titanium oxide, hafnium dioxide-alumina(HfO₂—Al₂O₃) alloy, other suitable high-k dielectric materials, and/orcombinations thereof. In some embodiments, the gate dielectric layer 102includes an interfacial layer formed between the channel layers and thedielectric material.

The gate dielectric layer 102 may be formed by CVD, ALD or any suitablemethod. In one embodiment, the gate dielectric layer 102 is formed usinga highly conformal deposition process such as ALD in order to ensure theformation of a gate dielectric layer having a uniform thickness aroundeach channel layer. The thickness of the gate dielectric layer 102 is ina range from about 1 nm to about 6 nm in one embodiment.

The gate electrode layer 104 is formed on the gate dielectric layer 102to surround each channel layer. The gate electrode 104 includes one ormore layers of a conductive material, such as polysilicon, aluminum,copper, titanium, tantalum, tungsten, cobalt, molybdenum, tantalumnitride, nickel silicide, cobalt silicide, TiN, WN, TiAl, TiAlN, TaCN,TaC, TaSiN, metal alloys, other suitable materials, and/or combinationsthereof.

The gate electrode layer 104 may be formed by CVD, ALD, electro-plating,or other suitable method. The gate electrode layer 104 is also depositedover the upper surface of the ILD layer 85. The gate dielectric layerand the gate electrode layer formed over the ILD layer 85 are thenplanarized by using, for example, CMP, until the top surface of the ILDlayer 85 is revealed.

In certain embodiments of the present disclosure, one or more workfunction adjustment layers (not shown) are interposed between the gatedielectric layer 102 and the gate electrode 104. The work functionadjustment layers are made of a conductive material such as a singlelayer of TiN, TaN, TaAlC, TiC, TaC, Co, Al, TiAl, HfTi, TiSi, TaSi orTiAlC, or a multilayer of two or more of these materials. For then-channel FET, one or more of TaN, TaAlC, TiN, TiC, Co, TiAl, HfTi, TiSiand TaSi is used as the work function adjustment layer, and for thep-channel FET, one or more of TiAlC, Al, TiAl, TaN, TaAlC, TiN, TiC andCo is used as the work function adjustment layer. The work functionadjustment layer may be formed by ALD, PVD, CVD, e-beam evaporation, orother suitable process. Further, the work function adjustment layer maybe formed separately for the n-channel FET and the p-channel FET whichmay use different metal layers.

As shown in FIGS. 34A and 34B, a cross sectional shape and an area of atleast one of the nanowires 27 is different from the remaining nanowiresin some embodiments. In certain embodiments, the uppermost nanowire 27 dhas a largest cross sectional area among the nanowires 27. In someembodiments, the uppermost nanowire 27 d has a teardrop shape, which isnot point symmetric, while the remaining nanowires have an oval shapewhich is point symmetric. In other embodiments, cross sectional shapesand areas of the nanowires 27 are different from each other.

It is understood that the GAA FETs undergoes further CMOS processes toform various features such as contacts/vias, interconnect metal layers,dielectric layers, passivation layers, etc.

FIGS. 35A-41B show an exemplary sequential operation for manufacturingthe GAA FET according to another embodiment of the present disclosure.It is understood that additional operations can be provided before,during, and after processes shown by FIGS. 35A-41B, and some of theoperations described below can be replaced or eliminated, for additionalembodiments of the method. The order of the operations/processes may beinterchangeable. Material, configuration, dimensions and/or processesthe same as or similar to the foregoing embodiments described withrespect to FIGS. 1-34B may be employed in the following embodiments, anddetailed explanation thereof may be omitted.

In this embodiment, before the source/drain epitaxial layer 80 isformed, the nanowires 27 are formed. After the structure shown in FIGS.15A-15C is formed, the processes as set forth in FIGS. 16A-26B arerepeated to form the fin structure 20 with several etched narrowportions. Then, the last channel cover layer and the hard mask 25 areremoved, thereby the structure shown in FIGS. 35A and 35B is obtained.Then, the exposed fin structure 20 with etched portions is oxidized toform nanowires 27 separated by oxide 90, by the operations the same asor similar to those explained with respect to FIGS. 32A and 32B. FIGS.36A and 36B show the structure after the oxide 90 is formed.

Then, as shown in FIGS. 37A and 37B, the oxide 90 is removed to releasethe semiconductor nanowires 27, by the operations the same as or similarto those explained with respect to FIGS. 33A and 33B. After thesemiconductor nanowires 27 are formed, a second sacrificial gatedielectric layer 72 is formed around each nanowire 27 (channel), and asecond sacrificial gate electrode 71 is formed on the gate dielectriclayer 72, as shown in FIGS. 38A and 38B. The second sacrificial gatedielectric layer 72 is made of silicon oxide formed by CVD and thesecond sacrificial gate electrode 71 is made of polysilicon or amorphoussilicon formed by CVD, in some embodiments.

Then, similar to FIGS. 29A and 29B, the SD cover layer 50 and hard mask25 are removed to expose a source/drain region of the fin structure 20,as shown in FIGS. 39A and 39B. Similar to FIGS. 30A and 30B, after asource/drain epitaxial layer 80 is formed over the source/drain regionof the fin structure 20, an interlayer dielectric (ILD) layer 85 isformed, as shown in FIGS. 40A and 40B. The source/drain epitaxial layer80 includes one or more layers of Si, SiP, SiC and SiCP for an n-channelFET or Si, SiGe and Ge for a p-channel FET. For the n-channel FET,phosphorus (P) may also be contained in the source/drain. For thep-channel FET, boron (B) may also be contained in the source/drain. Thesource/drain epitaxial layer 80 is formed by an epitaxial growth methodusing CVD, ALD or molecular beam epitaxy (MBE). In some embodiments, thefin structures of the source/drain regions are recessed down to aboutthe upper surface of the isolation insulating layer 30, and then thesource/drain epitaxial layer 80 is formed. After the material for theILD layer 85 is formed, a planarization operation, such as CMP, isperformed, so that the top portion of the second sacrificial gateelectrode 71 is exposed. Then, the second sacrificial gate electrode 71is removed, and the sacrificial gate dielectric layer 72 is removed, asshown in FIGS. 41A and 41B. Then, a gate dielectric layer and metal gateelectrode are formed similar to FIGS. 34A and 34B.

FIGS. 42-46 show an exemplary sequential operation for manufacturing theGAA FET according to another embodiment of the present disclosure. It isunderstood that additional operations can be provided before, during,and after processes shown by FIGS. 42-46, and some of the operationsdescribed below can be replaced or eliminated, for additionalembodiments of the method. The order of the operations/processes may beinterchangeable. Material, configuration, dimensions and/or processesthe same as or similar to the foregoing embodiments described withrespect to FIGS. 1-41B may be employed in the following embodiments, anddetailed explanation thereof may be omitted.

After the structure shown in FIGS. 15A-15C are formed, the processes asset forth are repeated to form the fin structure 20 with several etchednarrow portions. FIG. 42 shows a structure after the last channelsidewall spacers 67 are formed. Then, as shown in FIG. 43, part of thechannel sidewall spacers 67 is removed so that part of the channelsidewall spacers 67 remains only at narrowed portions of the finstructure 20 as remaining sidewalls 68. In some embodiments, one or moreisotropic etching operations are utilized.

Then, the exposed fin structure 20 with the remaining channel sidewalls68 is oxidized to form nanowires 28 separated by oxide 92 as shown inFIG. 44. In some embodiments, one or more of a thermal oxidizationprocess, a plasma oxidization process and/or a chemical oxidizationprocess are utilized. In some embodiments, a process temperature of thethermal oxidization is in a range from about 500° C. to about 800° C. Insome embodiments, a process temperature of the plasma oxidization is ina range from about 300° C. to about 500° C. The remaining channelsidewalls 68 protect the portions of the fin structure to be nanowires28 during the oxidation of the fin structure 20.

Next, as shown in FIG. 45, the oxides 92 are removed, and further theremaining channel sidewalls 68 are removed as shown in FIG. 46, therebyreleasing the nanowires. In some embodiments, one or more additionaletching operations are performed on the nanowires 28 to round corners ofthe nanowires 28.

In some embodiments, after the structure shown in FIGS. 30A and 30B isformed and then the sacrificial layer 70 is removed to obtain thestructure shown in FIG. 42. In such a case, after the nanowires 28 areformed, the operations explained with respect to FIGS. 34A and 34B areperformed. In other words, after the source/drain epitaxial layer 80 isformed, the nanowires 28 are formed. In other embodiments, before thesacrificial layer 69 shown in FIGS. 27A and 27B is formed, the structureshown in FIG. 42 is obtained and the nanowires 28 are formed as setforth above. In such a case, the operations explained with respect toFIGS. 38A-41B are performed. In other words, before the source/drainepitaxial layer 80 is formed, the nanowires 28 are formed in someembodiments.

FIGS. 47-52 show an exemplary sequential operation for manufacturing theGAA FET according to another embodiment of the present disclosure. It isunderstood that additional operations can be provided before, during,and after processes shown by FIGS. 47-52, and some of the operationsdescribed below can be replaced or eliminated, for additionalembodiments of the method. The order of the operations/processes may beinterchangeable. Material, configuration, dimensions and/or processesthe same as or similar to the foregoing embodiments described withrespect to FIGS. 1-46 may be employed in the following embodiments, anddetailed explanation thereof may be omitted.

FIG. 47 is the same as FIG. 26B. In this embodiment, the etching toreduce the width of the fin structures is performed such that the upperportion 20 a of the fin structure 20 is separated from the bottomportion 20 b as shown in FIG. 48. Then, the third channel sidewallspacers 65 are removed as shown in FIG. 49. It is noted that the upperportion 20 a of the fin structure is supported at least by the sidewallspacers 45. Then, the second insulating layer is optionally recessed toexpose an upper portion of the bottom portion 20 b of the fin structureas shown in FIG. 50 in some embodiments. Next, an oxidization process isperformed to form nanowires 27 as shown in FIG. 51, by the same orsimilar operations explained with respect to FIGS. 32A and 32B and FIGS.36A and 36B. Then, the oxide 91 is removed, thereby releasing thenanowires 27 as shown in FIG. 52. In the foregoing embodiment, after thethird channel sidewall spacers 65 are formed, the separation process toseparate the upper portion 20 a and the bottom portion 20 b isperformed. In other embodiments, after the last channel sidewallspacers, which may be the fourth, fifth, . . . , etc., are formed theseparation process to separate the upper portion 20 a and the bottomportion 20 b is performed.

FIGS. 53A-77B show an exemplary sequential operation for manufacturingthe GAA FET according to another embodiment of the present disclosure.It is understood that additional operations can be provided before,during, and after processes shown by FIGS. 53A-77B, and some of theoperations described below can be replaced or eliminated, for additionalembodiments of the method. The order of the operations/processes may beinterchangeable. Material, configuration, dimensions and/or processesthe same as or similar to the foregoing embodiments described withrespect to FIGS. 1-52 may be employed in the following embodiments, anddetailed explanation thereof may be omitted.

In the following embodiments, a fin structure is sculpted before asacrificial gate structure is formed.

Similar to FIG. 2, a semiconductor fin structure 120 with a hard mask125 is formed over a semiconductor substrate 110, as shown in FIG. 53A.Then, as shown in FIGS. 54A and 54B, a first insulating layer 130 isformed over the fin structure 120. A material for the first insulatinglayer 130 is formed to fully cover the fin structure 120 and aplanarization operation, such as CMP, is performed to expose the hardmask 125. The first insulating layer 130 includes silicon oxide, siliconnitride, silicon oxynitride (SiON), SiOCN, SiCN, fluorine-doped silicateglass (FSG), or a low-k dielectric material, formed by LPCVD (lowpressure chemical vapor deposition), plasma-CVD or flowable CVD.

Next, as shown in FIGS. 55A and 55B, the first insulating layer 130 isrecessed to expose an upper portion of the fin structure 120. The recessetching includes one or more dry etching and/or wet etching operations.The exposed amount D11, which is a distance between the top of the finstructure 120 and the upper surface of the recessed first insulatinglayer 130, is about 5 nm to about 30 nm in some embodiments.

Then, a first cover layer 160 made of one of SiN, SiCN, SiON and SiC isformed as shown in FIGS. 56A and 56B. In some embodiments, the firstcover layer 160 is made of the different material than the firstinsulating layer. In some embodiments, the first cover layer 160 is madeof the same material as the hard mask 125.

Further, as shown in FIGS. 57A and 57B, anisotropic etching is performedto form first sidewall spacers 161. Then, as shown in FIGS. 58A and 58B,the first insulating layer 130 is further recessed by one or more dryetching and/or wet etching operations to expose a part of the finstructure 120. The exposed amount D12, which is a distance between thebottom of the first sidewall spacers 161 and the upper surface of therecessed first insulating layer 130, is about 5 nm to about 30 nm insome embodiments.

Next, as shown in FIGS. 59A-59B, the exposed portion of the finstructure 20 is sculpted by etching to reduce the width of the exposedportion. In some embodiments, wet etching using TMAH or KOH is used toetch the exposed portion. In other embodiments, dry etching is used. Bythis etching, the narrowest portion 122 of the sculpted fin structure120 has a width W11 which is about 30% to about 70% of the originalwidth of the fin structure 120 in some embodiments.

Then, as shown in FIGS. 60A and 60B, the first insulating layer 130 isfurther recessed to further expose a portion of the fin structure 120.The recess etching includes one or more dry etching and/or wet etchingoperations. The exposed amount D13 is substantially equal to or smallerthan D11 in some embodiments. The exposed amount D13 is about 5 nm toabout 20 nm in some embodiments.

Then, a second cover layer 162 made of one of SiN, SiCN, SiON and SiC isformed as shown in FIGS. 61A and 61B. In some embodiments, the firstchannel sidewall spacer 161 is removed before the formation of thesecond cover layer 162. In other embodiments, the first channel sidewallspacer 161 is not removed before the formation of the second cover layer162. In some embodiments, the second cover layer 162 is made of the samematerial as the first cover layer 160.

Further, as shown in FIGS. 62A and 62B, anisotropic etching is performedto form second sidewall spacers 163. Then, as shown in FIGS. 63A and63B, the first insulating layer 130 is further recessed by one or moredry etching and/or wet etching operations to expose a part of the finstructure 120. The exposed amount D14, which is a distance between thebottom of the second sidewall spacers 163 and the upper surface of therecessed first insulating layer 130, is about 5 nm to about 20 nm insome embodiments. In some embodiments, D14 is substantially equal toD12.

Next, as shown in FIGS. 64A and 64B, the exposed portion of the finstructure 120 is sculpted by being partially etched to reduce the widthof the exposed portion, similar to FIGS. 59A and 59B.

The operations of forming a cover layer, recessing the first insulatinglayer and etching (sculpting) the exposed fin structure are repeated bythe desired number of times, for example 3-10 times in total. Thus, asculpted fin structure 120 is formed in the channel region and thesource/drain regions.

FIGS. 65A and 65B show a structure after the last cover layer 167 isformed and the last sculpting operation is performed. Then, a fin coverlayer 149 is formed as shown in FIGS. 66A and 66B. In some embodiments,the fin cover layer 149 is made of the same material as the first tolast cover layers, and includes one or more layers of SiN, SiCN, SiONand SiC. Next, as shown in FIGS. 67A and 67B, the fin cover layer ispatterned to expose a channel region of the sculpted fin structure andto form an SD cover layer 150.

Then, as shown in FIGS. 68A and 68B, a sacrificial gate dielectric layer142 is formed over the sculpted fin structure 120, and a sacrificiallayer 139 is formed. Then, one or more planarization operations, such asan etch back operation and a CMP operation, are performed to form afirst sacrificial gate electrode 144, as shown in FIGS. 69A and 69B. Insome embodiments, the first sacrificial gate electrode 144 is made ofpolysilicon or amorphous silicon formed by CVD. The sacrificial gatedielectric layer 142 is made of silicon oxide by CVD.

Then, the SD cover layer is removed, and an insulating material layer140 for gate sidewall spacers is formed as shown in FIGS. 70A and 70B.The insulating material layer 140 includes one or more layers ofinsulating material, such as SiN, SiON, SiOC, SiOCN and SiCN or anyother suitable insulating material. SiC may be used as well. Theinsulating material layer 140 can be formed by ALD or CVD, or any othersuitable method. Then, as shown in FIGS. 71A and 71B, anisotropicetching is performed to form sidewall spacers 145. FIG. 71B shows across sectional view along the Y direction cutting the source/drainregion. As shown in FIGS. 71A and 71B, remaining portions 147 of theinsulating material layer 140 exist in the sculpted portions of the finstructure, and the remaining portions 147 are subsequently removed byone or more dry etching and/or wet etching operations, as shown in FIGS.72A and 72B. FIG. 72B shows a cross sectional view along the Y directioncutting the source/drain region. In some embodiments, the sidewallspacers 145 are also slightly etched and thus the width thereof becomessmaller.

Then, as shown in FIGS. 73A and 73B, a source/drain epitaxial layer 180is formed over the source/drain region of the sculpted fin structure120. FIG. 73B shows a cross sectional view along the Y direction cuttingthe source/drain region. The source/drain epitaxial layer 180 includesone or more layers of Si, SiP, SiC and SiCP for an n-channel FET or Si,SiGe and Ge for a p-channel FET. For the n-channel FET, phosphorus (P)may also be contained in the source/drain. For the p-channel FET, boron(B) may also be contained in the source/drain. The source/drainepitaxial layer 180 is formed by an epitaxial growth method using CVD,ALD or molecular beam epitaxy (MBE). Further, as shown in FIGS. 74A and74B, an ILD layer 155 is formed. FIG. 74B shows a cross sectional viewalong the Y direction cutting the source/drain region. The materials forthe ILD layer 155 include compounds comprising Si, O, C and/or H, suchas silicon oxide, SiON, SiCOH and SiOC. Organic materials, such aspolymers, may be used for the ILD layer 155. After the material for theILD layer 155 is formed, a planarization operation, such as CMP, isperformed, so that the top portion of the first sacrificial gateelectrode 144 and the sacrificial gate dielectric layer 142 are exposed.Then, the first sacrificial gate electrode 144 and the sacrificial gatedielectric layer 142 are removed, as shown in FIGS. 75A and 75B. FIG.75B shows a cross sectional view along the Y direction cutting thechannel region.

Next, the exposed sculpted fin structure 120 is oxidized to formnanowires 127 separated by oxide 190 as show in FIGS. 76A and 76B. FIG.76B shows a cross sectional view along the Y direction cutting thechannel region. In some embodiments, as shown in FIGS. 76A and 76B, fournanowires 127 a-127 d are formed, but the number of nanowires is notlimited to four. The oxidization process is performed such that theetched narrow portions of the sculpted fin structure 120 are fullyoxidized, while non-etched portions of the sculpted fin structure 120are only partially oxidized. In some embodiments, one or more of athermal oxidization process, a plasma oxidization process and/or achemical oxidization process are utilized. In some embodiments, aprocess temperature of the thermal oxidization is in a range from about500° C. to about 800° C. In some embodiments, a process temperature ofthe plasma oxidization is in a range from about 300° C. to about 500° C.The ILD layer 155 protects the S/D structures 180 during the oxidationof the exposed fin structure 120.

Then, as shown in FIGS. 77A and 77B, the oxide 190 is removed to releasethe semiconductor nanowires 127. FIG. 77B shows a cross sectional viewalong the Y direction cutting the channel region. After thesemiconductor nanowires 127 are formed, a gate dielectric layer isformed around each nanowire 127 and a gate electrode layer is formed onthe gate dielectric layer, similar to FIGS. 34A and 34B. It isunderstood that the GAA FETs undergoes further CMOS processes to formvarious features such as contacts/vias, interconnect metal layers,dielectric layers, passivation layers, etc.

In some embodiments, before the source/drain epitaxial layer is formed,the sculpted fin structures of the source/drain regions are recesseddown to about the upper surface of the first insulating layer 130, andthen the source/drain epitaxial layer 181 is formed, as shown in FIG.78, which shows a cross sectional view along the Y direction cutting thesource/drain region.

FIGS. 79A-87C show an exemplary sequential operation for manufacturingthe GAA FET according to another embodiment of the present disclosure.It is understood that additional operations can be provided before,during, and after processes shown by FIGS. 79A-87B, and some of theoperations described below can be replaced or eliminated, for additionalembodiments of the method. The order of the operations/processes may beinterchangeable. Material, configuration, dimensions and/or processesthe same as or similar to the foregoing embodiments described withrespect to FIGS. 1-78 may be employed in the following embodiments, anddetailed explanation thereof may be omitted.

FIGS. 79A and 79B are the same as FIGS. 71A and 71B. Then, a second SDcover layer 157 is formed as shown in FIGS. 80A and 80B. FIG. 80B showsa cross sectional view along the Y direction cutting the source/drainregion. In some embodiments, the SD cover layer 157 includes one or morelayers of SiN, SiCN, SiON and SiC.

Then, the first sacrificial gate electrode 144 and the sacrificial gatedielectric layer 142 are removed to expose the sculpted fin structure120. Next, the exposed sculpted fin structure 120 is oxidized to formnanowires 127 separated by oxide 190 as show in FIGS. 81A and 81B,similar to FIGS. 76A and 76B. FIG. 81B shows a cross sectional viewalong the Y direction cutting the channel region. In some embodiments,as shown in FIGS. 81A and 81B, four nanowires 127 a-127 d are formed,but the number of nanowires is not limited to four. The oxidizationprocess is performed such that the etched narrow portions of thesculpted fin structure 120 are fully oxidized, while non-etched portionsof the sculpted fin structure 120 are only partially oxidized. In someembodiments, one or more of a thermal oxidization process, a plasmaoxidization process and/or a chemical oxidization process are utilized.In some embodiments, a process temperature of the thermal oxidization isin a range from about 500° C. to about 800° C. In some embodiments, aprocess temperature of the plasma oxidization is in a range from about300° C. to about 500° C. The second SD cover layer 157 protects thesource/drain regions of the fin structure 120 during the oxidation ofthe channel region of the exposed fin structure 120.

Then, as shown in FIGS. 82A and 82B, the oxide 190 is removed to releasethe semiconductor nanowires 127. FIG. 82B shows a cross sectional viewalong the Y direction cutting the channel region. After thesemiconductor nanowires 127 are formed, a sacrificial gate dielectriclayer 172 is formed around each nanowire 127 and a sacrificial layer 169is formed on the gate dielectric layer 172, as shown in FIGS. 83A and83B. Then, one or more planarization operations, such as an etch backoperation and a CMP operation, are performed to form a secondsacrificial gate electrode 170 over the sacrificial gate dielectriclayer 172, as shown in FIGS. 84A and 84B.

Subsequently, the second SD cover layer 157 is removed and the remainingportions 147 of the insulating material layer 140 are removed from thesource/drain regions, as shown in FIGS. 85A and 85B. FIG. 85B shows across sectional view along the Y direction cutting the source/drainregion. In some embodiments, the remaining portions 147 of theinsulating material layer 140 remain under the sidewall spacers 145.

Then, similar to FIGS. 73A and 73B, a source/drain epitaxial layer 180is formed over the source/drain region of the sculpted fin structure120, as shown in FIGS. 86A and 86B. FIG. 86B shows a cross sectionalview along the Y direction cutting the source/drain region.

Further, as shown in FIGS. 87A-87C, an ILD layer 185 is formed over thesource/drain epitaxial layer 180. FIG. 87B shows a cross sectional viewalong the Y direction cutting the channel region and FIG. 87C shows across sectional view along the Y direction cutting the channel regionsource/drain region. In some embodiments, before the source/drainepitaxial layer is formed, the sculpted fin structures of thesource/drain regions are recessed down to about the upper surface of thefirst insulating layer 130, and then the source/drain epitaxial layer181 is formed, similar to FIG. 78. Then, the second sacrificial gateelectrode 170 and the sacrificial gate dielectric layer 172 are removed,and a gate dielectric layer and a metal gate electrode are formed,similar to FIGS. 34A and 34B.

FIGS. 88-93 show an exemplary sequential operation for manufacturing theGAA FET according to another embodiment of the present disclosure. It isunderstood that additional operations can be provided before, during,and after processes shown by FIGS. 88-93, and some of the operationsdescribed below can be replaced or eliminated, for additionalembodiments of the method. The order of the operations/processes may beinterchangeable. Material, configuration, dimensions and/or processesthe same as or similar to the foregoing embodiments described withrespect to FIGS. 1-87C may be employed in the following embodiments, anddetailed explanation thereof may be omitted.

FIG. 88 shows a structure the same as that of FIGS. 65A and 65B. FIG. 88is a cross sectional view along the Y direction cutting the source/drainregion. Then, an oxidization operation is performed to fully oxidize thebottommost sculpted portion of the fin structure 120 to form oxide 194,as shown in FIG. 89. The oxidization operation is the same as or similarto that for making channel nanowires as set forth above. By theoxidation process, the fin structure 120 is divided into an upperportion 120 a and a bottom portion 120 b. Subsequently, themanufacturing operations explained with respect to FIGS. 66A-71B areperformed. FIG. 90 shows a cross sectional view along the Y directioncutting the source/drain region, after the remaining portions 147 areformed. Then, as shown in FIG. 91, which is a cross sectional view alongthe Y direction cutting the source/drain region, the remaining portions147 are removed, similar to FIGS. 72A and 72B. Further, as shown in FIG.92, which is a cross sectional view along the Y direction cutting thesource/drain region, a source/drain epitaxial layer 180 is formed tocover the upper portion 120 a of the fin structure. In this embodiment,the source/drain region of the fin structure with the epitaxial layer iselectrically separated by the oxide 194 from the bottom portion of thefin structure 120 b and the substrate 110. At the channel region, anoxidation operation explained with respect to FIGS. 81A and 81B isperformed and then semiconductor nanowires 127 are formed. FIG. 93 showsa cross sectional view along the Y direction cutting the channel region,after the oxide 190 is formed.

FIGS. 94-100 show an exemplary sequential operation for manufacturingthe GAA FET according to another embodiment of the present disclosure.It is understood that additional operations can be provided before,during, and after processes shown by FIGS. 94-100, and some of theoperations described below can be replaced or eliminated, for additionalembodiments of the method. The order of the operations/processes may beinterchangeable. Material, configuration, dimensions and/or processesthe same as or similar to the foregoing embodiments described withrespect to FIGS. 1-93 may be employed in the following embodiments, anddetailed explanation thereof may be omitted.

In the foregoing embodiments, the fin structures 20 and 120 are formedby etching a bulk silicon substrate (silicon wafer). In the forgoingembodiments, a silicon germanium (SiGe) channel is utilized for, inparticular, a p-type GAA FET. A sculpted fin structure is formed from aSiGe fin structure.

FIG. 94 shows the same structure as FIGS. 2, 53A and 53B, in which a finstructure 220 formed by etching a silicon substrate 210 using a hardmask 215 is shown. Then, an insulating layer 230 is formed as shown inFIG. 95. The insulating layer 230 is the same as or similar to theisolation insulating layer 30 or the first insulating layer 130.

Next, the hard mask 215 and an upper portion of the fin structure 220 isremoved by etching to form a space 222, as shown in FIG. 96. Then, aSiGe fin structure 225 is epitaxially formed in the space 222, as shownin FIG. 97. In some embodiments, the SiGe fin structure is made ofSi_(1-x)Ge_(x), where x is more than about 0.1 to about 1.0. In someembodiments, one or more buffer layers made of Si_(1-y)Ge_(y), where y<xis formed between the etched fin structure 220 and the SiGe finstructure 225.

Next, an insulating layer 239 is formed over the SiGe fin structure 235and the insulating layer 230 as shown in FIG. 98, and then one or moreplanarization operations, such as CMP, are performed to expose theinsulating layer 230 as shown in FIG. 99. With this operation, a capinsulating layer 240 is formed on the SiGe fin structure 235.

Then, the insulating layer 230 is recessed as shown in FIG. 100, whichcorresponds to the structure of FIGS. 55A and 55B. In some embodiments,the insulating layer 230 is further recessed to expose the entire SiGefin structure, which corresponds to the structure of FIG. 3.Subsequently, the operations to form a sculpted fin structure andsemiconductor nanowires are performed to manufacture a GAA FET.

In some embodiments, after at least two structures of FIG. 95 areformed, one of the structures is processed to manufacture a SiGe finstructure for a p-type GAA FET with the operations explained withrespect to FIGS. 96-100. On the other hand, one of the structures iscovered by a cover layer during the operations to form a p-type GAA FET,and after the cover layer is removed, the operations for manufactures ann-type GAA FET are performed.

The various embodiments or examples described herein offer severaladvantages over the existing art. For example, in the presentdisclosure, nanowires can be manufactured without using a stacked layerstructure, such as Si/SiGe, and thus it is possible to simplify amanufacturing process and to reduce manufacturing cost.

It will be understood that not all advantages have been necessarilydiscussed herein, no particular advantage is required for allembodiments or examples, and other embodiments or examples may offerdifferent advantages.

In accordance with an aspect of the present disclosure, in a method ofmanufacturing a semiconductor device, a fin structure is formed over asubstrate. The fin structure is sculpted to have a plurality ofnon-etched portions and a plurality of etched portions having a narrowerwidth than the plurality of non-etched portions. The sculpted finstructure is oxidized so that a plurality of nanowires are formed in theplurality of non-etched portions, respectively, and the plurality ofetched portions are oxidized to form oxides. The plurality of nanowiresare released by removing the oxides. In one or more of the foregoing andthe following embodiments, the sculpting the fin structure includes (i)covering the fin structure except for an exposed portion correspondingto one of the plurality of etched portions, and (ii) etching the exposedportion to form the one of the plurality of etched portions. In one ormore of the foregoing and the following embodiments, (i) and (ii) arerepeated twice or more to form the plurality of etched portions. In oneor more of the foregoing and the following embodiments, (i) and (ii) arerepeated from a portion corresponding to an uppermost one of theplurality of etched portions to a portion corresponding to a bottommostone of the plurality of etched portions. In one or more of the foregoingand the following embodiments, in (i), a lower portion of the finstructure below the exposed portion is covered by a first insulatinglayer, and an upper portion of the fin structure above the exposedportion is covered by a channel cover layer. In one or more of theforegoing and the following embodiments, wherein the insulating layerincludes silicon oxide. In one or more of the foregoing and thefollowing embodiments, the channel cover layer includes one of SiN,SiCN, SiON and SiC. In one or more of the foregoing and the followingembodiments, the fin structure includes a channel region andsource/drain regions, and during the sculpting, the source/drain regionsare covered by a source/drain cover layer. In one or more of theforegoing and the following embodiments, the source/drain cover layerand the channel cover layer are made of the same material. In one ormore of the foregoing and the following embodiments, the source/draincover layer and the channel cover layer are made of different materialfrom each other. In one or more of the foregoing and the followingembodiments, the source/drain cover layer includes one of SiN, SiCN,SiON and SiC. In one or more of the foregoing and the followingembodiments, after the sculpting, a sacrificial gate structure is formedto cover the sculpted fin structure, the source/drain cover layer isremoved, source/drain epitaxial layers are formed over the source/drainregions of the fin structure, the source/drain epitaxial layers arecovered with a dielectric layer, and the sacrificial gate structure isremoved. After the sacrificial gate structure is removed, the oxidizingand the releasing are performed, and a gate dielectric layer is formedover each of the released nanowires and a gate electrode layer is formedover the gate dielectric layer. In one or more of the foregoing and thefollowing embodiments, a fin cover layer is disposed between thesacrificial gate structure and the sculpted fin structure. In one ormore of the foregoing and the following embodiments, during thesculpting, the oxidizing and the releasing, the source/drain regions arecovered by the source/drain cover layer. Further, after the releasing, asacrificial gate structure is formed over the released nanowires, thesource/drain cover layer is removed, source/drain epitaxial layers areformed over the source/drain regions of the fin structure, thesource/drain epitaxial layers are covered with a dielectric layer, thesacrificial gate structure are removed, and a gate dielectric layer isformed over each of the nanowires and forming a gate electrode layerover the gate dielectric layer. In one or more of the foregoing and thefollowing embodiments, the oxidizing is performed by one of thermaloxidation, plasma oxidation and chemical oxidation.

In accordance with another aspect of the present disclosure, in a methodof manufacturing a semiconductor device, a fin structure is formed overa substrate. The fin structure is sculpted to have a plurality ofnon-etched portions and a plurality of etched portions having a narrowerwidth than the plurality of non-etched portions. The sculpted finstructure is covered with a fin cover layer. Etching on the fin coverlayer is performed so that remaining portions of the fin cover layerexist in the plurality of etched portions. The sculpted fin structure isoxidized so that a plurality of nanowires are formed in the plurality ofetched portions, respectively, and the plurality of none-etched portionsare oxidized to form oxides. The plurality of nanowires are released byremoving the oxides. The remaining portions of the fin cover layer areremoved. In one or more of the foregoing and the following embodiments,the sculpting the fin structure includes (i) covering the fin structureexcept for a portion corresponding to one of the plurality of etchedportions, (ii) etching the exposed portion to form the one of theplurality of etched portions, and repeating (i) and (ii) twice or moreto form the plurality of etched portions. In one or more of theforegoing and the following embodiments, in (i), a lower portion of thefin structure below the exposed portion is covered by a first insulatinglayer, and an upper portion of the fin structure above the exposedportion is covered by a channel cover layer. In one or more of theforegoing and the following embodiments, the insulating layer and thechannel cover layer are made of different materials from each other.

In accordance with another aspect of the present disclosure, in a methodof manufacturing a semiconductor device, a fin structure is formed overa substrate. The fin structure is sculpted to have a plurality ofnon-etched portions and a plurality of etched portions having a narrowerwidth than the plurality of non-etched portions. A bottommost one of theplurality of etched portions is removed. The sculpted fin structure isoxidized so that a plurality of nanowires are formed in the plurality ofnon-etched portions, respectively, and the plurality of etched portionsare oxidized to form oxides. The plurality of nanowires are released byremoving the oxides.

In accordance with one aspect of the present disclosure, a semiconductordevice includes a plurality of semiconductor wires, a gate dielectriclayer wrapping around each of the plurality of semiconductor wires, anda gate electrode layer disposed over the gate dielectric layer. A crosssectional shape of an uppermost one of the plurality of semiconductorwires has a tear-drop shape and has a largest area among the pluralityof semiconductor wires.

The foregoing outlines features of several embodiments or examples sothat those skilled in the art may better understand the aspects of thepresent disclosure. Those skilled in the art should appreciate that theymay readily use the present disclosure as a basis for designing ormodifying other processes and structures for carrying out the samepurposes and/or achieving the same advantages of the embodiments orexamples introduced herein. Those skilled in the art should also realizethat such equivalent constructions do not depart from the spirit andscope of the present disclosure, and that they may make various changes,substitutions, and alterations herein without departing from the spiritand scope of the present disclosure.

What is claimed is:
 1. A semiconductor device, comprising: a pluralityof semiconductor wires; a gate dielectric layer wrapping around each ofthe plurality of semiconductor wires; and a gate electrode layerdisposed over the gate dielectric layer, wherein a cross sectional shapeof an uppermost one of the plurality of semiconductor wires has atear-drop shape and has a largest area among the plurality ofsemiconductor wires.
 2. The semiconductor device of claim 1, whereinremaining ones of the plurality of semiconductor wires have an ovalshape.
 3. The semiconductor device of claim 1, further comprising: asource/drain region which is a source/drain semiconductor fin structure;an isolation insulating layer from which the source/drain semiconductorfin structure protrudes; sidewall spacers disposed on opposite sidefaces of the gate electrode layer; and a dielectric layer, differentfrom the gate dielectric layer, disposed between the gate electrodelayer and the isolation insulating layer.
 4. The semiconductor device ofclaim 3, wherein the dielectric layer is made of a different materialthan the sidewall spacers.
 5. The semiconductor device of claim 3,further comprising: a bottom fin structure over which the plurality ofsemiconductor wires are disposed, wherein the bottom fin structure and abottom part of the source/drain semiconductor fin structure arecontinuously formed.
 6. The semiconductor device of claim 5, wherein thegate dielectric layer is disposed on a top of the bottom fin structure.7. The semiconductor device of claim 6, wherein the top of the bottomfin structure is rounded.
 8. The semiconductor device of claim 3,wherein the source/drain semiconductor fin structure includes recessedportions under one of the sidewall spacers.
 9. The semiconductor deviceof claim 8, wherein the recessed portions are located at levels betweenadjacent ones of the plurality of semiconductor wires.
 10. Thesemiconductor device of claim 1, wherein a cross sectional shape of abottommost one of the plurality of semiconductor wires has a smallestarea among the plurality of semiconductor wires.
 11. A semiconductordevice, comprising: a plurality of semiconductor wires; a bottom finstructure protruding from a semiconductor substrate, over which theplurality of semiconductor wires are disposed; a gate dielectric layerwrapping around each of the plurality of semiconductor wires; a gateelectrode layer disposed over the gate dielectric layer; a source/drainregion which is a source/drain semiconductor fin structure asource/drain epitaxial layer wrapping the source/drain semiconductor finstructure; an isolation insulating layer from which the source/drainsemiconductor fin structure protrudes; and sidewall spacers disposed onopposite side faces of the gate electrode layer, wherein the bottom finstructure and the source/drain semiconductor fin structure arecontinuously formed of a same semiconductor material.
 12. Thesemiconductor device of claim 11, wherein a cross sectional shape of anuppermost one of the plurality of semiconductor wires has a tear-dropshape and has a largest area among the plurality of semiconductor wires.13. The semiconductor device of claim 12, wherein a cross sectionalshape of a bottommost one of the plurality of semiconductor wires has asmallest area among the plurality of semiconductor wires.
 14. Thesemiconductor device of claim 11, further comprising: a dielectriclayer, different from the gate dielectric layer, disposed between thegate electrode layer and the isolation insulating layer, wherein thedielectric layer is made of a different material than the sidewallspacers.
 15. The semiconductor device of claim 11, wherein the gatedielectric layer is disposed on a top of the bottom fin structure. 16.The semiconductor device of claim 18, wherein the top of the bottom finstructure is rounded.
 17. The semiconductor device of claim 11, whereina width of the bottom fin structure is greater than a width of each ofthe plurality of semiconductor wires.
 18. A semiconductor device,comprising: a plurality of semiconductor wires; a bottom fin structureprotruding from a semiconductor substrate, over which the plurality ofsemiconductor wires are disposed; a gate dielectric layer wrappingaround each of the plurality of semiconductor wires; a gate electrodelayer disposed over the gate dielectric layer; an isolation insulatinglayer from which the source/drain semiconductor fin structure protrudes;sidewall spacers disposed on opposite side faces of the gate electrodelayer; and a dielectric layer, made of a different material than thegate dielectric layer and the sidewall spacers, disposed between thegate electrode layer and the isolation insulating layer.
 19. Thesemiconductor device of claim 18, wherein the bottom fin structure andthe source/drain semiconductor fin structure are continuously formed ofa same semiconductor material.
 20. The semiconductor device of claim 18,wherein the dielectric layer includes SiON or SiOC.